1. Field of the Invention:
This invention relates generally to acoustical resonators, and more particularly the invention relates to housing and acoustical couplers for use with such resonators.
2. Prior Art:
Mechanical or acoustical resonators are well known devices having applications as filters and as temperature sensors, for example. Disclosed in U.S. Pat. No. 3,318,152 issued to Thompson et al is one such temperature sensor.
Particularly in temperature sensing applications, acoustical resonators are placed in environments where hermetic sealing of the resonator is imperative. Co-pending application Ser. No. 955,634, filed Oct. 30, 1978, now U.S. Pat. No. 4,233,843, discloses a temperature sensing system employing double mode acoustical resonators and which has particular application in sensing the temperature of a high power electrical transformer. In this application the resonator is placed in the oil within the transformer, and temperature of the transformer is determined by measuring the acoustical response of the resonator.
In addition to the need for hermetic sealing of the resonator within a housing, the waveguides which couple acoustical waves to and from the resonator must pass through the resonator housing. Often spurious signals are introduced by coupling between the housing and the waveguide. Additionally, a waveguide which is large enough to present minimum attenuation to acoustical waves will not have the proper source impedance for the resonator, resulting in reflections and poor efficiency unless a suitable transition section is employed.